Shock absorber



J- A.l STEVENS v SHOCK ABsoRBER Filed Nov. 5' 1926 Patented Jan. 3, 192.8.

UNITED STATES 1,655,216 PATENT OFFICE.

JOHN A. STEVENS, OF LOWELL, MASSACHUSETTS, ASSIGNOR TC STEVENS PRODUCTS COMPANY, OF LOWELL, MASSACHUSETTS, A. CORFORATION OF DELAWARE.

SHOCK ABSOR-BER.

Application filed November 5, 1926.

This invention 4relates to shock absorbers for vehicles and other uses and more particularly to improvements in fluid compression devices or shock absorbers of the hydropneumatic type embodying dash-pot action together with cushioning by means of fluid pressure.

The type of shock absorber which employs a gas, such as air, under pressure for cushion ing shocks or jars together With a liquid dash-pot or hydraulically operated checking means for retarding the movements of the shock absorbeiI are particularly ineffective in counteracting or smoothing out severe jolts, or a series of sudden j olts for the reason that this form of compression device as heretofore produced acts sluggishly or slowly` which is due to the inherent nature or action of the resistance ports employed in the device. In this forni of device sluggish action can not be rectified or improved by enlarging the resistance ports for the reason that although by this ineaiis the shock absorber Will be more effective in .operation in connection Witli the more severe jolts, it would be practically ineffective for slight jolts and the vehicle Wouldbe vsubjected to more or less continuous vibrations in passing over the ordinary uneven surfaces.

The forms of device heretofore employed of the type above referred to are particularly subject to leakage of pressure fluid because of the diiiiculty of confining the fluid under .the high pressure which. is employed and which is necessary in order to provide for the usual variations in load to Which trucks and busses, particularly the more modern double decked busses, are subjected.

The cushioning which is produced under light loads or even with ordinary loads by shock absorbers in which high pressure fluid is employed is particularly ineffective and the operation of such shock absorbers is therefore unsatisfactory. Many unsuccessful attempts have been made to overcome the defects of shock absorbers of this type, and in connection with lighter vehicles this form of shock absorber has frequently been replaced by the all-spring form of shock absorber. ever While being satisfactory for light loads is not adapted for use in connect-ion with heavyy busses or trucks, Which are subjected to change from no load to loads of about 5000 pounds in the case ofy busses, and usually This form of shock absorber how-y Serial N o. 146,357.

from no load to about 10000 pounds in the case of trucks. The all-spring form of shock absorber is unadapted foi' busses or trucks carrying such heavy loads because of the fact that the vibrations which were set up Were not effectively dampened even by the use of auxiliary snubbers. Under heavy loads this form of shock absorber is wholly iueifective in connection with shocks of unusual severity because of the coming` together of metallic parts Which is liable to cause breakage of the shock absorber or the parts to which it is connected.

is a result of a large numberI of experiments upon various types of shock absorbers have devised means which are practically effective in connection With shock absorbers ofthe pneumatic or hydro-pneumatic type, by means of Which such shock absorbers may carry loads greatly in excess of the ordinary loads and provide effective cushioning even under the heaviest loads Without danger of the coming together of metallic parts. Moreover by the means which I have devised a comparatively low fluid pressure may be eniployed in the shock absorber cylinder so as to minimize the danger of leakage. Furthermore the means ivhich I have devised is so arranged as to be inoperative under ordinary or light loads and to come into action only With loads greater than a predetermined load or in the case of encountering unusually severe olts. The device provides also means for assisting in checking the rebound in a shock absorber so that tlie rebound is taken up not only by means of the hydraulically operating dashpot but by means operating entirely independently thereof. The means which I have devised provides therefore for independently adjusting the means for taking up the rebound ivhereby the device may be so adjusted that a rapid operation will take place, the device not only being effective onk light loads but also under the heavier loads so substantially to prevent the shocks or jars due to the inequalities in the road over which 'the vehicle passes.

One of the objects of my invention is to provide improvements in shock absorbers of the hydraulically operated type by which the device is rendered more effective in opera` tion and by means of which it is adapted not only for light loads but also for the heaviest loads to which the vehicle may be subjected.

Another object of the invention is to provide improvements in shock absorbers of the forni having combined pressure fluid and hydraulic or dash-pot operation whereby the dash-pot portion of the device may bev speed-y decrease of pressure fluid in the device.

Y Another object of the invention is to pro-y vide in the hydraulically controlled form of shock absorber positive means to assist in cushioning the rebound o-f the shock absorber. j' v With these and other objects in view the invention comprises the various features herein described and defined in the claims.

The invention is illustrated in its pre-y ferred forni in the accompanying drawings in which:

Fig. l1 is a cross sectional view in elevationof a shock absorber embodying my invention;

Fig. 2 is a view illustrating the manner in which the device may be mounted; and

'Fig 8 is a detail section of the plunger on the line 3-8 in Fig. 1.

Referring more in detail to the drawings the numeral 2 designates the shock absorber as a whole, which may be attached or con- Vnected in the usual way to a leaf spring 4v and a bracket 6, by means of which it may be connected to the chassis of a vehicle or other body to which it is to be applied. The numeral 8 designates the outside casing of the shock absorberV to which the bracket 6 may be attached as indicated more particularly. in Fig. 2. The outer cylinder por, casing` screw-threaded connection 10to an inner cylinder 12 which has a head or cap portion 14 in which is the usual valve 16, by means lof which pressure fluid may be forcedinto the device. Mounted so as to slide between the cylinders 8 and 12 is an intermediate cylinder member 18, which is directly con.

nected to the leaf spring 4. llhe lower portion of the inner casing or cylinder 12 is of a size so as to fit tightly within the cylinder 18, thereby serving as a guide member for the` sliding vcylinder during relative movements of the cylinder 18 and the cylin- V 6o ders 12 and V8. YThe cylinder 12 has connected thereto a plunger or piston 2() which carries a cup leather packing 22 so as to provide ya tight sliding joint between the piston and the inner surface of the cylinder 18. The cup leather packing may be lars 36 and 88 8 is attached preferably by a` pressed into engagement with the inner surface of'cylinder 18 by' means ofa conical expander or ring 24, which is pressed up wardly by means of a spring member 26. The spring is .preferably seated in a groove 28 in the base of a threaded nut 30, which is preferably attached in place on the lower end of the piston by means of screw-threaded'connections 82. The piston 20 is preferably provided with a movablek plunger 84 which vserves as a single actingY pump during operation of the shock absorber to pump oil fromvpassageway 46 to passageway 54 in its downward movement.` On the upper part ofthe pump plunger 34 are two colwhich are secured Yto the plunger. Between the two collars is a disk member 40 which is free to slide on the pump plungervand adapted to engage an opening 41 in the "piston 20. Above the collar 86 is a coil spring 42 which bears on one 'side againstv a stationary member or holding member 44, connectedv to the inner cylinder 12, andwhich presses downwardly on the collar 86Y soas to hold4 the plunger yieldably in contact with a screw plug at the lower end of the plunger 20.

In th-e upper portion of the piston 20 is an annular chamber 46 :which is in open communication with the inner surface of the cylinder' 18, this annular chamber serving to catch oil that leaks past the packing 22 due to the pressure within the device. Between the bore in which the plunger l84 moves andthe annular chamber 46 is a passageway 48 in which is a ball valve 50 adapted to 'seat upwardly against the vseat 52 and in the passageway 54, which'connects the bore in which the plunger moves with the space 56' in theupper portion of the piston, is a ball valve 58. 'When plunger 34 rises, oil is drawn past valve 50 into the bottomV of` the plunger opening and when the plunger again descends, this oil is forced past valve 58 into passageway 54, thereby" returning leakage oil to the main body of oil. lt is accordingly obvious that thie plunger 34 cooperates with the check valves 50l and58,l and the related passages vin'returning oil from the groove 46 to the main body of oil. rThis function is highly desirable since, otherwise,in the course of time,"a consider-L ableV body of oil would tend to form above the packing and would eventually serve to choke the breather mechanism 64.

In the walls o-l the cylinder 8' is a pas. sagewayV 60 leading -from the lower portion of the cylinder into the space between the cylinder 18 and cylinder 8, which is connected to the usual form of breather 62, having Va valve `64'connected thereto, thereby. providing for the admission of filtered air.V At the lower end of the Vpassageway 60 is thepurpose of injecting oil into ythe duct loe liu

Cil

or passageway 60 for lubricating purposes. The device thus far described is of known construction and operation need not theretore be described in detail, a device of this general character being disclosed for example in the patent to Lieubau, No. 1,519,851.

In the space between the cylinders 8 and l2 and preferably mounted on the cylinder 18 is a superimposed load spring 68 which is of such a length that when the cylinder' is inliated to the normal pressure so as to carry the normal loadthe spring will be free, or in other'words there will be no load on the spring. The spring 68 is preferably mounted upon the upper surface of the cylinder 18 being held in place by means of' a. flange or circular projection 69. The spring :is preferably of such a size and is so mounted that it will carry a portion of the load only after a predetermined maximum load to be carried by the pneumatic pressure has been reached. lilith loads in excessvof this predetermined load a proportional partthereof will be carried by the spring the amount carried depending upon the size or strength of the spring and the amount of its deflection from its no load position. Asthe telescoping cylinders move closer together the air pressure or fluid pressure becomes greater, the pressure exerted by the gas or air being proportional to the decrease in volume in the shock absorber, in accordance with the well known law of gases. lf, for example, through the addition of load to the vehicle the shock absorber is compressed to one-third of the volume occupied by the air or gas under normal load, then the pressure exerted by the gas at this load will be three times that exerted under normal load. 'lf the length of the spring G8 is so positioned with relation to the inner cylinder 18 and the top of the inner chamber 70 that the spring will be compressed when the normal or ordinary load is exceeded then if the spring has been compressed for example to the position at which the pressure exerted by the pressure fluid is three times that at the normal load position, the force exerted by the spring will be an amount depending upon the'spring constant and the distance which the spring has been compressed; in other words, the force exerted by the spring will be a constant multiplied by the deflection of the spring from its no load position. The load on the vehicle will therefore be carried partly by the spring and partly by the pressure of the fluid in the cylinder in cases where the load is in excess of the normal or predetermined load. the proportion of' the load carried by each Vdepending upon the volume of the cylinder, the spring constant and other well known factors. Then a sudden load is impressed upon the absorber through the vehicle passing over a bump in the road, for example, the jolt is taken up by both the spring and the fluid compres sion in the shock absorber. In order to assist in cushioning the shock return movement to the normal position, l provide a spring 72y which is preferably mounted in a space between the cylinder 18 and the inner surface of the cylinder 8, the spring being of such a size as to substantially lit around the cylinder 18. The spring is preferably seated at its lower end on a shoulder 7l formed at substantially the midportion of the outer casing or guide member 8. At the upper end of the cylinder 18 is an outwardly extending annular ring or projecting portion 76 on which the upper portion of the spring 72 is adapted to seat. In the downward movement of the cylinder 18 relative to the outer cylinder 8, or in other words during` the rebound of the shock absorber, the spring member 72 is compressed and assists in neutralizing the force of the rebound. The neutralization of the rebound force is also partly accomplished by means of the low of oil through the piston to cushion the downward movement ot' the cylinder 18. During ,the upward or opposite movement of the cylinder 18 the oil inthe lower portion ol' the cylinder is forced upwardly through the oil passageways in the piston 20'. and thus assists in preventing vibration of the device.

In using the shock absorber it is first charged with oil or other sealing liquid while in the collapsed position through the opening or valve 1G in the head 1l, the cylinder being filled preferably to a height above the lower edge of the member The shock absorber is then inflated with air or other pressure fluid through the valve under the cap 16, the air pressure which is preferably employed being suiiicient to carry the average or ordinary load. When the device is operated through compression thereof, the relative downward movement of the piston 2() causes a current of oil to flow through passageway 3) in the plunger into the passageway 56 in an upward direction which causes the disk 40 to be raised until it strikes the collar 36, lifting the pump plunger 34 against the force of the spring 42. iVhen the shock absorber expands or moves in the opposite direction the oil will flow downwardly through the passageway 56 whereby the disk l() will be carried in the reverse or downward direction, until it strikes the collar 88 which forces the oil pump 34 to the bottom of the stroke causing the oil which was drawn into the pump in the reverse movement to be discharged back into the interior of the shock absorber. During the compression movement of the shock absorber air will be drawn through the breather G2 into the annular space between the cylinders 18 and 8, and when the shock absorber is again expanded the air will be absorber in ite` lili) ling any dirt or foreign particles which may lll have become lodged betweenV the cylinders.

. By 'the use of the means which has been described, shock absorbers of the hydropneuinatic ytype may be caused to act rapidly and efficiently on heavy or light loads, or on intermediate loads producing arsi'nooth noiseless operation, in place'ot the snapping or cracking sound generally produced by shock absorbers or this type when the vehicle to which they are attached receives a sudden jolt. Moreover, by the use or a pressure in the cylinders which is designed to carry the average load instead or the heaviest load to which vehicle may be subjected the diiiiculties produced in coniining the high operating pressures are obviated, and the riding qualities of the vehicle are greatly improved. Furthermore, by the use oit moderately low pressure in place or' the high pressure heretoi'ore generally employed the danger ot' leakage of the cushioning duid from the shock absorbers is reduced to a minimum and through the combination with the auxiliary' cushioning or supporting means which become operative only with excessive loads or in the case ot unusually severe jolts, the vehicle to which they are attached ride with the saine evennesss both loaded and unloaded.

y 1t is to be understood that thel Jform ot the device which has been described may be varied as will be apparent to those skilled in the art without departing from the spirit Y or scope of the invention as defined in the claims.

l claim: Y Y

1. A shock absorber having a piston cyltions and to carry proportionally increasing loads under loads in excess of 'a predeterinined'aniount or under subnormal niation r of the cylinders, and a second spring mount*- edl so as to oppose expansive movements of said cylinders 'roin normal load position.

shock absorber comprising an upper a closed upper end, a lower cylinder adapted to ltit outside ot and telescope with the upper cylindery and having a closed lower end, a non-compressible liuid normally lilling the space defined by 'the cylinders toa level above the bottom ot' Ythe upper cylinder, means on the upper cylinder forv preventing leakage of theviiuid between the cylinders, a compressible fluid lilling the remainder of the space within the upper cylinder', two abutments fixed with respect to the upper cylinder, a main spring extending from a point on the lower cylinder and normally terminating short of one of said abutments, whereby it will be inoperative on relatively slight shocks but etiective on relatively heavy shocks to actin parallel with the compressible fluid in opposing the initial shock, and a second spring extending between a point fixed with respect to the lower cylinder and the other ol said abutments to cushion the recoil from the initial shock. Y Y Signed by me at Lowell, Massachusetts this 2nd day ot November, 1926.

. J OHN A. STEVENS.

cylinder having (Sli 

